G Force Pilot Training And Swbo

[samdive]

Saw a TV doc last night about pilots training to not black out under increasing amounts of G Force. It said that they can learn to tense up their upper body to keep the blood in their brain and thus push up the limit at which they black out

any lessons here for avoiding Shallow Water Black Out?

 

[Alun]

this is Hook breathing... it works for freediving. but in my opinion, if you need to use it to maintain consciousness then you're pushing yourself too close to the limit...

 

[shaneshac]

Is SWB not due to lack of oxygen as opposed to lack of blood pressure in brain?

My opinion is that keeping the tension in the upper body would be no use if there is no oxygen present in the blood. It would also burn more oxygen and increase the chances of SWB

A hook breathe is different as you are bearing down on a breathe of fresh air to make it reach the brain ASAP.

My $0.02

 

[samdive]

shaneshac - bearing down to push more blood pressure to the brain is what they seemed to be doing rather than hook breathing (which incidentally makes me cough so I gave up!)

any hints on how to do that? would it help?

 

[shaneshac]

Ok this is as technical as I can put it.

The high G-force experienced by pilots causes the blood to pool in the legs and torso, removing pressure form the brain. The low blood pressur in the brain cuases the pilot to pass out, even when breathing pure oxygen.

The pilots learn to tense their bodies and hence constrict the arteries and veins within their bodies. This keeps the pressure in the brain higher and keeps pilot conscious.

SWB on the other hand is caused by lack of oxygen. No matter how much you tense your body, if there is no oxygen you will pass out. To my knowledge there is no loss of blood pressure to brain on surfacing.

A hook breathe helps divers as it pushes the oxygen from the breathe, into the blod supply faster than a normal breathe. This will allow a diver to avoid Samba or BO.

In summary, pilot training does not work as far as I know.

Please correct me ppl if I am wrong

 

[samdive]

sounds like you are right for SWBO but there have also been cases of people blacking out at depth after making too violent a turn (and blood pressure dropping in brain)
maybe we could use the pilot thing at that stage!

 

[shaneshac]

Its true, In fact I once went real light headed after making a turn at 18m.

I suppose it would have to be tried as making your body so tense goes against the whole freediving philosofy.

Then again, so much internal pressure can also cause you to black out (i.e overpacking)

So doing this movement at depth might be dangerous

 

[chojan]

SWB on the other hand is caused by lack of oxygen. No matter how much you tense your body, if there is no oxygen you will pass out. To my knowledge there is no loss of blood pressure to brain on surfacing.

In the very last part of your ascent, when your lungs are expanding rapidly and to full+pack, I had understood that there can be a reduction in blood supply to the brain due to increasing chest wall pressure on the arteries.

More of the issue is probably the "vacuum effect", where a fast increase in lung volume will cause a large PO2 gradient into the lung which will tend to reduce blood PO2 quickly.

I am sure someone else will be able to correct me on this.

 

[efattah]

First of all, even when you black out, you still have about 4% O2 in your lungs, and about 40% of your hemoglobin is still saturated with oxygen, so there is still plenty of oxygen in your blood.

When it comes to oxygen availability to tissues, all that matters is pressures, not quantities. So, increasing the blood pressure in your head (or decreasing it), has a dramatic effect on the O2 availability to brain cells. This is why a person with low blood pressure blacks out so much more easily than a person with normal blood pressure.

Contractions act to increase the blood pressure in your head. I think that is their main purpose; the body is trying to increase the O2 availability to brain cells. Some may argue against that hypothesis, but contractions are definitely not your body 'just trying to breathe', since they happen on exhale statics as well, at a time when inhaling would be the correct action, not exhaling.

So, I definitely think any tricks fighter pilots use could help you delay a blackout. I personally have found that a deliberate and prolonged abdominal 'contraction' to force blood into my head helps my vision clear up at the end of a long apnea.


Eric Fattah
BC, Canada

 

[Alun]

the only time i've ever started to grey out was actually due to high Gs in an aircraft! :yack ... i've never experienced it when freediving.

 

[shaneshac]

HI Eric,

Do you not agree then that contracting your whole body to keep the blood pressure high, would increase oxygen metabolism and hence be counter productive?